1. Field of Invention
This invention relates to a temperature compensated oscillator, a control method for a temperature compensated oscillator, and a wireless communication device.
2. Description of Related Art
Conventionally, as oscillators used for electronic equipment, such as wireless communication devices, a temperature compensated oscillator (TCXO) is used because the output of frequency signals needs to be stable over a wide temperature range.
This temperature compensated oscillator utilizes the fact that oscillation frequency of a piezoelectric resonator changes according to the load capacity in order to maintain the oscillation frequency constant through a temperature compensation circuit in which the load capacity is varied according to temperature.
Also, among the temperature compensated oscillators, there are analog oscillators where the temperature compensation circuit is constructed by an analog circuit, and digital oscillators where the temperature compensation circuit is constructed by a digital circuit.
In an analog temperature compensated oscillator, because the temperature compensated circuit consists of many resistor elements and semiconductor elements, noise Vn is added to the temperature compensation voltage Vc1 output by the temperature compensation circuit due to thermal noise, shot noise, and the like.
Therefore, in the analog temperature compensated oscillator shown in FIG. 15, by inserting a filter circuit 2 that removes the high-frequency component between a temperature compensation circuit 3 and a voltage controlled oscillation circuit 4, noise Vn can be removed from the output voltage Vc1+Vn of the temperature compensation circuit 3.
In this way, by installing the filter circuit 2 that removes noise contained in the temperature compensation voltage Vc1 output from the temperature compensation circuit 3, phase noise of the output signal is reduced.
FIG. 16 is a block diagram of a digital temperature compensated oscillator.
In a digital temperature compensated oscillator 10, a temperature compensation circuit 11 consists, for example, of a temperature sensor 11A, an analog/digital (AID) converter 11B, a memory 11C, and a digital/analog (D/A) converter 11D.
In the temperature compensation circuit 11, temperature information measured by the temperature sensor 11A is converted from analog to digital by the A/D converter 11B, converted to digital signal for compensating the temperature property of a piezoelectric resonator X memorized in advance in the memory 11C, converted from digital to analog by the D/A converter 11D, and output as temperature compensation voltage Vc1.
In this case, if any change occurs to the digital signal input to the D/A converter 11D due to temperature change, step-shape noise Vn occurs to the temperature compensation voltage Vc1 due to influence of resolution of the D/A converter 11D.
Because of this, as shown in FIG. 16, by inserting the filter circuit 2 that removes the high-frequency component between the temperature compensation circuit 11 and the voltage controlled oscillation circuit (VCXO) 4, noise Vn is removed from the temperature compensation voltage Vc1.
Therefore, by using a filter circuit such as an analog one in a digital temperature compensated oscillator, phase noise of the output signal can be reduced.
As in a property curve of a filter circuit (LPF), such as that shown in FIG. 17, the larger the time constant, namely the lower the cut-off frequency fc, the more decline high frequency shows in a filter circuit.
Because of this, for reducing phase noise of output signals of a temperature compensated oscillator using a filter circuit, it is better to set the cut-off frequency fc of the filter circuit low. Here, shown in FIG. 18 is a property curve between the SSB phase noise at the detuning frequency and cut-off frequency fc of a filter circuit.
On the other hand, when power is supplied intermittently to a temperature compensated oscillator, from a power-saving point of view as in the standing-by time for a portable wireless communication device, reduction of time from the oscillation start until the output frequency becomes stable (called xe2x80x9cOscillation starting timexe2x80x9d below) is desired.
However, as in a property curve of the oscillation starting time shown in FIG. 19, the lower the cut-off frequency of a filter circuit is set, the longer the oscillation starting time Tsta becomes.
Because of this, in a temperature compensated oscillator, there is a problem that realization of both reduction of phase noise of the output signal and reduction of the oscillation starting time is difficult.
Also, as shown in FIG. 20, common as an oscillator of modem portable wireless communication devices is a VC-TCXO that is equipped with a frequency control voltage input terminal VC for the frequency adjustment function that adjusts the frequency even more precisely based on the signal from the base station.
Namely, as shown in FIG. 20, VC-TCXO 12 inputs a frequency control signal xcfx86VC supplied to a signal processing circuit of a portable wireless communication device based on the signal received from the base station, and converts the voltage of this frequency control signal xcfx86VC to a frequency control voltage Vc2 by a voltage conversion circuit 13.
Then, in VC-TCXO 12, the frequency control voltage Vc2 and temperature compensation voltage Vc1 are added by an adder 14 that is supplied to a voltage controlled oscillation circuit 4 via the filter circuit 2. By this, frequency of the output signal is temperature compensated and changed to the frequency synchronous to the base frequency of the base station.
In the circuit described above, if phase noise of the output signal is reduced using a filter circuit 2 with a large time constant, a problem also occurs in that response of the oscillation frequency to the frequency control voltage Vc2 is not good.
One objective of this invention is to at least provide a temperature compensated oscillator where phase noise of the output signal can be reduced, frequency of the output signal stabilizes in a short time, and response of the control is good. In accordance with various exemplary embodiments of this invention, a method of controlling and a wireless communication device equipped with this temperature compensated oscillator are provided.
In accordance with one exemplary embodiment of this invention, a temperature compensated oscillator is provided that has a voltage controlled oscillation circuit whose output signal oscillation frequency changes according to supplied voltage, and a temperature compensation circuit that outputs temperature compensation voltage for keeping the oscillation frequency of the output signal constant based on temperature.
filter circuit that removes noise contained in the temperature compensation voltage;
switching circuit connected in parallel with the filter circuit; and
power control circuit that controls power supply at least to the voltage controlled oscillation circuit and the temperature compensation circuit, respectively,
wherein the power control circuit turns on the switching circuit for a specified period when power supply to the voltage controlled oscillation circuit is started.
In accordance with another exemplary embodiment of this invention, a temperature compensated oscillator is provided that has a voltage controlled oscillation circuit whose output signal oscillation frequency changes according to supplied voltage and a temperature compensation circuit that outputs temperature compensation voltage for keeping the output signal oscillation frequency constant based on temperature, comprising;
filter circuit for removing noise contained in the temperature compensation circuit that is a low-pass filter where capacitance elements are connected in parallel to resistor elements via a switching circuit; and
power control circuit that controls power supply at least to the voltage controlled oscillation circuit and the temperature compensation circuit, respectively,
wherein the switching circuit is circuit for switching the connection locations of one end of all of the capacitance elements between the temperature compensation voltage output side and the temperature compensation voltage input side of the resistor elements, and the power control circuit connects by the switching circuit one end of the capacitance elements to the temperature compensation voltage input side of the resistor elements when power supply to the voltage controlled oscillation circuit is started and to the temperature compensation voltage output side of the resistor elements after a specified period has passed.
In accordance with another exemplary embodiment of this invention, a temperature compensated oscillator is provided that has a voltage controlled oscillation circuit whose output signal oscillation frequency changes according to supplied voltage and a temperature compensation circuit that outputs temperature compensation voltage for keeping the output signal oscillation frequency constant based on temperature. The temperature compensated oscillator may include a filter circuit that removes noise contained in the temperature compensation circuit that is a plurality of stages of low-pass filters where capacitance elements are connected in parallel to resistor elements via a switching circuit, and a power control circuit that controls power supply at least to the voltage controlled oscillation circuit and the temperature compensation circuit, respectively. The switching circuit is a circuit for switching the connection locations of one end of all of the capacitance elements between the temperature compensation voltage output side of each corresponding resistor element and the temperature compensation voltage input side of the resistor element closest to the temperature compensation circuit among all of the resistor elements. The power control circuit connects, by the switching circuit, one end of all of the capacitance elements to the temperature compensation voltage input side of the resistor element closest to the temperature compensation circuit when power supply to the voltage controlled oscillation circuit is started, and to the temperature compensation voltage output side of each corresponding resistor element after a specified period has passed.
In accordance with another exemplary embodiment of this invention, in the temperature compensated oscillator described above, inductance elements are used in place of the resistor elements in the filter circuit.
In accordance with another exemplary embodiment of this invention, the temperature compensated oscillator described above has an output switching circuit between the temperature compensation circuit and the filter circuit which can switch between a first mode where the output voltage follows the temperature compensation voltage, and a second mode where the output voltage is maintained at the temperature compensation voltage of the mode switching time. The power control circuit switches the output switching circuit to the first mode when power supply to the temperature compensation circuit is started and the output switching circuit to the second mode when power supply to the temperature compensation circuit is stopped.
In accordance with another exemplary embodiment of this invention, a temperature compensated oscillator is provided that has a voltage controlled oscillation circuit whose output signal oscillation frequency changes according to supplied voltage and a temperature compensation circuit that outputs temperature compensation voltage for keeping the output signal oscillation frequency constant based on temperature. The temperature compensated oscillator may include anoutput switching circuit which can switch between a first mode where the output voltage follows the temperature compensation voltage, and a second mode where the output voltage is maintained at the temperature compensation voltage of the mode switching time, a filter circuit that removes noise contained in the temperature compensation voltage output via the output switching circuit, and a power control circuit that controls power supply at least to the voltage controlled oscillation circuit and the temperature compensation circuit, respectively. The power control circuit switches the output switching circuit to the first mode when power supply to the temperature compensation circuit is started, and to the second mode when power supply to the temperature compensation circuit is stopped.
In accordance with another exemplary embodiment of this invention, in the temperature compensated oscillator described above, the power control circuit stops power supply to the circuits, except the output switching circuit, when power supply to the voltage controlled oscillator and the temperature compensation circuit are stopped.
In accordance with another exemplary embodiment of this invention, a temperature compensated oscillator is provided that has a voltage controlled oscillation circuit whose output signal oscillation frequency changes according to supplied voltage, a temperature compensation circuit that outputs temperature compensation voltage for keeping the output signal oscillation frequency constant based on temperature, a voltage control circuit that outputs frequency control voltage for making the output signal oscillation frequency the frequency to be set based on the externally supplied frequency control signal, and an adder that outputs the temperature compensation voltage and the frequency control voltage added together. The temperature compensated oscillator may include a first filter circuit that removes noise contained in the temperature compensation voltage, a switching circuit connected in parallel with the first filter circuit, a second filter circuit that removes noise contained in the frequency control voltage, and a power control circuit that controls power supply at least to the voltage controlled oscillation circuit and the temperature compensation circuit, respectively. The power control circuit turns on the switching circuit for a specified period when power supply to the voltage controlled oscillation circuit is started.
In accordance with another exemplary embodiment of this invention, a temperature compensated oscillator is provided that has a voltage controlled oscillation circuit whose output signal oscillation frequency changes according to supply voltage, a temperature compensation circuit that outputs temperature compensation voltage for keeping the output signal oscillation frequency constant based on temperature, a voltage control circuit that outputs frequency control voltage for making the output signal oscillation frequency the frequency to be set based on the externally supplied frequency control signal, and an adder that outputs the temperature compensation voltage and the frequency control voltage added together. The temperature compensated oscillator may include a first filter circuit that is a circuit for removing noise contained in the temperature compensation voltage and is a low-pass filter where capacitance elements are connected in parallel to resistor elements, a second filter circuit that removes noise contained in the frequency control voltage, and a power control circuit that controls power supply at least to the voltage controlled oscillation circuit and the temperature compensation circuit, respectively. A switching circuit is provided for switching the connection locations of one end of all of the capacitance elements between the temperature compensation voltage output side and the temperature compensation voltage input side of the resistor elements. The power control circuit connects, by the switching circuit, one end of the capacitance elements to the temperature compensation voltage input side of the register elements when power supply to the voltage controlled oscillation circuit is started, and to the temperature compensation voltage output side of the resistor elements after a specified period has passed.
In accordance with another exemplary embodiment of this invention, a temperature compensated oscillator is provided that has a voltage controlled oscillation circuit whose output signal oscillation frequency changes according to supplied voltage, a temperature compensation circuit that outputs temperature compensation voltage for keeping the output signal oscillation frequency constant based on temperature, a voltage control circuit that outputs frequency control voltage for making the output signal oscillation frequency the frequency to be set based on the externally supplied frequency control signal, and an adder that outputs the temperature compensation voltage and the frequency control voltage added together. The temperature compensated oscillator may include a first filter circuit that is a circuit for removing noise contained in the temperature compensation voltage and is a low-pass filter of plural number of stages where capacitance elements are connected in parallel to resistor elements, a second filter circuit that removes noise contained in the frequency control voltage, and a power control circuit that controls power supply at least to the voltage controlled oscillation circuit and the temperature compensation circuit, respectively. The switching circuit is a circuit for switching the connection locations of one end of all of the capacitance elements between the temperature compensation voltage output side of each corresponding resistor element and the temperature compensation voltage input side of the resistor element closest to the temperature compensation circuit among all of the resistor elements. The power control circuit connects, by the switching circuit, one end of the capacitance elements to the temperature compensation voltage input side of the resistor element closest to the temperature compensation circuit when power supply to the voltage controlled oscillation circuit is started, and to the temperature compensation voltage output side of each corresponding resistor elements after a specified period has passed.
In accordance with another exemplary embodiment of this invention, in the temperature compensated oscillator described above, an inductance element is used in place of the resistance element in the first filter circuit.
In accordance with another exemplary embodiment of this invention, the temperature compensated oscillator described above has, between the temperature compensation circuit and the filter circuit, an output switching circuit that can switch between a first mode where the output voltage follows the temperature compensation voltage, and a second mode where the output voltage is maintained at the temperature compensation voltage of the mode switching time. The power control circuit switches the output switching circuit to the first mode when power supply to the temperature compensation circuit is started, and to the second mode when power supply to the temperature compensation circuit is stopped.
In accordance with another exemplary embodiment of this invention, a temperature compensated oscillator is provided that has a voltage controlled oscillation circuit whose output signal oscillation frequency changes according to supplied voltage, a temperature compensation circuit that outputs temperature compensation voltage for keeping the output signal oscillation frequency constant based on temperature, a voltage control circuit that outputs frequency control voltage for making the output signal oscillation frequency the frequency to be set based on the externally supplied frequency control signal, and an adder that outputs the temperature compensation voltage and the frequency control voltage added together. The temperature compensated oscillator may include an output switching circuit that can switch between a first mode where the output voltage follows the temperature compensation voltage, and a second mode where the output voltage is maintained at the temperature compensation voltage of the mode switching time, a first filter circuit that removes noise contained in the temperature compensation voltage output via the output switching circuit, a second filter circuit that removes noise contained in the frequency control voltage, and a power control circuit that controls power supply at least to the voltage controlled oscillation circuit and the temperature compensation circuit, respectively. The power control circuit switches the output switching circuit to the first mode when power supply to the temperature compensation circuit is started, and to the second mode when power supply to the temperature compensation circuit is stopped.
In accordance with another exemplary embodiment of this invention, in the temperature compensated oscillator described above, the power control circuit stops power supply to circuits, except the output switching circuit, when power supply to the voltage controlled oscillation circuit and the temperature compensation circuit are stopped.
In accordance with another exemplary embodiment of this invention, in the temperature compensated oscillator described in above, the cut-off frequency of the second filter circuit is higher than the cut-off frequency of the first filter circuit.
In accordance with another exemplary embodiment of this invention, in the temperature compensated oscillator described above, the second filter circuit consists of resistor elements and capacitance elements, respectively.
In accordance with another exemplary embodiment of this invention, in the temperature compensated oscillator described above, the second filter circuit consists of inductance elements and capacitance elements, respectively.
In accordance with another exemplary embodiment of this invention, in the temperature compensated oscillator described above, the power control circuit controls power supply to the voltage controlled oscillation circuit and the temperature compensation circuit based on the externally supplied control signal.
In accordance with another exemplary embodiment of this invention, in the temperature compensated oscillator described above, the power control circuit starts power supply to the voltage controlled oscillation circuit and the temperature compensation circuit at the same time, and the power supply is stopped at the same time.
In accordance with another exemplary embodiment of this invention, in the temperature compensated oscillator described above, the voltage controlled oscillation circuit has an oscillation circuit for oscillating an piezoelectric resonator, and a variable capacitance element whose capacitance changes according to the voltage supplied.
In accordance with another exemplary embodiment of this invention, in the temperature compensated oscillator described above, component parts except the piezoelectric resonator are constructed as one-chip IC.
In accordance with another exemplary embodiment of this invention, in the temperature compensated oscillator described above, the one-chip IC and the piezoelectric resonator are stored in one package.
In accordance with another exemplary embodiment of this invention, the temperature compensated oscillator described above operates based on the output signal of the temperature compensated oscillation circuit.
In accordance with another exemplary embodiment of this invention, a method is provided for controlling a temperature compensated oscillator that has a voltage controlled oscillation circuit whose output signal oscillation frequency changes according to the supplied voltage and a temperature compensation circuit that outputs temperature compensation voltage for keeping the output signal oscillation frequency constant based on temperature. The method may include removing noise contained in the temperature compensation voltage using a filter circuit, and controlling power supply at least to the voltage controlled oscillation circuit and the temperature compensation circuit, respectively, using a power control circuit. The power control circuit turns on a switching circuit connected in parallel with the filter circuit only for a specified period when power supply to the voltage controlled oscillation circuit is started.
In accordance with another exemplary embodiment of this invention, the method for controlling a temperature compensated oscillator described above includes switching between a first mode where the output voltage follows the temperature compensation voltage, and a second mode where the output voltage is maintained at the temperature compensation voltage of the mode switching time, using an output switching circuit between the temperature compensation circuit and the filter circuit. The power control circuit switches the output switching circuit to the first mode when power supply to the temperature compensation circuit is started, and switches the output switching circuit to the second mode when power supply to the temperature compensation circuit is stopped.
In accordance with another exemplary embodiment of this invention, a method is provided for controlling a temperature compensated oscillator that has a voltage controlled oscillation circuit whose output signal oscillation frequency changes according to the supplied voltage and a temperature compensation circuit that outputs temperature compensation voltage for keeping the output signal oscillation frequency constant based on temperature. The method may include switching between a first mode where the output voltage follows the temperature compensation voltage, and a second mode where the output voltage is maintained at the temperature compensation voltage of the mode switching time, using an output switching circuit, removing noise contained in the temperature compensation voltage output via the output switching circuit using a filter circuit, and controlling power supply at least to the voltage controlled oscillation circuit and the temperature compensation circuit, respectively, using a power control circuit. The power control circuit switches the output switching circuit to the first mode when power supply to the temperature compensation circuit is started, and to the second mode when power supply to the temperature compensation circuit is stopped.
In accordance with another exemplary embodiment of this invention, in the method for controlling a temperature compensated oscillator described above, the power control circuit stops power supply to circuits, except the output switching circuit, when power supply to the voltage controlled oscillation circuit and the temperature compensation circuit are stopped.
In accordance with another exemplary embodiment of this invention, a method is provided for controlling a temperature compensated oscillator that has a voltage controlled oscillation circuit whose output signal oscillation frequency changes according to supplied voltage, a temperature compensation circuit that outputs temperature compensation voltage for keeping the output signal oscillation frequency constant based on temperature, a voltage control circuit that outputs frequency control voltage for making the output signal oscillation frequency the frequency to be set based on the externally supplied frequency control signal, and an adder that outputs the temperature compensation voltage and the frequency control voltage added together. The method may include removing noise contained in the temperature compensation voltage using a first filter circuit, removing noise contained in the frequency control voltage using a second filter circuit, and controlling power supply to the voltage controlled oscillation circuit and the temperature compensation circuit, respectively, using a power control circuit. The power control circuit turns on a switching circuit connected in parallel with the first filter circuit for a specified period when power supply to the voltage controlled oscillation circuit is started.
In accordance with another exemplary embodiment of this invention, the method for controlling a temperature compensated oscillator described above includes switching between a first mode where the output voltage follows the temperature compensation voltage, and a second mode where the output voltage is maintained at the temperature compensation voltage of the mode switching time, using an output switching circuit between the temperature compensation circuit and the first filter circuit. The power control circuit switches the output switching circuit to the first mode when power supply to the temperature compensation circuit is started, and to the second mode when power supply to the temperature compensation circuit is stopped.
In accordance with another exemplary embodiment of this invention, a method is provided for controlling a temperature compensated oscillator that has a voltage controlled oscillation circuit whose output signal oscillation frequency changes according to supplied voltage, a temperature compensation circuit that outputs temperature compensation voltage for keeping the output signal oscillation frequency constant based on temperature, a voltage control circuit that outputs frequency control voltage for making the output signal oscillation frequency the frequency to be set based on externally supplied frequency control signal, and an adder that outputs the temperature compensation voltage and the frequency control voltage added together. The method may include switching between a first mode where the output voltage follows the temperature compensation voltage, and a second mode where the output voltage is maintained at the temperature compensation voltage of the mode switching time, using an output switching circuit, removing noise contained in the temperature compensation voltage output via the output switching circuit using a first filter circuit, removing noise contained in the frequency control voltage using a second filter circuit, and controlling power supply at least to the voltage controlled oscillation circuit and the temperature compensation circuit, respectively, using a power control circuit. The power control circuit switches the output switching circuit to the first mode when power supply to the temperature compensation circuit is started, and to the second mode when power supply to the temperature compensation circuit is stopped.
In accordance with another exemplary embodiment of this invention, in the method for controlling a temperature compensated oscillator described above, the power control circuit stops power supply to circuits, except the output switching circuit, when power supply to the voltage controlled oscillation circuit and the temperature compensation circuit are stopped.
In accordance with another exemplary embodiment of this invention, in the method for controlling a temperature compensated oscillator described above, the power control circuit controls power supply to the voltage controlled oscillation circuit and the temperature compensation circuit based on externally supplied control signals.